As methods to observe a transparent and colorless living cell and living tissue, a method to observe the living cell in a state as it is using a phase contrast microscope, a differential interference contrast microscope and the like, a method to form and dye a thin strip samples from a living tissue and observe them with a bright field microscope, a method to observe a thin strip sample using a phase contrast microscope, a differential interference contrast microscope and the like without dyeing have been known. Meanwhile, a method to observe a living tissue and the like using a differential interference contrast microscope is disclosed in Japanese Laid-open Patent Publication No. 09-015504 and the like.
Other than these, a method to observe a living cell and a living tissue with a fluorescence confocal microscope after dyeing them with a fluorochrome, or making the living cell and the living tissue express fluorescent protein such as GFP (Green Fluorescent Protein) by gene transfer has also been known. Since a fluorescence confocal microscope has a good three-dimensional resolution, when observing a living tissue, it is possible to observe the three-dimensional structure without forming any strip sample. For this reason, currently, the fluorescent observing method using a fluorescence confocal microscope is most popular as a method used in observing the fine three-dimensional structure of a living cell and living tissue.
Incidentally, due to the emergence of pluripotent stem cells such as iPS cells (induced pluripotent stem cells) and ES cells (embryonic stem cells) that enables regeneration of tissues of and nerves of organs by induction of differentiation, it is expected that regenerative medicine to cure a number of disorders by transplanting tissues and nerves of organs regenerated with iPS cells and ES cells into the living body becomes possible. Then, studies for its clinical application are under way.
The mutation of iPS cells and ES cells themselves, or, the mutation occurring in tissues and the like regenerated by induction of differentiation of the cells such as tumorigenic transformation is not desirable especially in the clinical application in regenerative medicine and should be avoided. For this reason, in the studies for clinical application, efforts have been made to check mutation and alteration in each process from the cell level to the tissue and organ to be regenerated.